The invention relates to a process for the hydroformylation of an ethylenically unsaturated compound in the presence of an acid with a pKa less than +3, and a catalyst of a group VIII metal and a bidentate ligand.
Processes for the hydroformylation of ethylenically unsaturated compounds are known in the art. In U.S. Pat. No. 5,004,823 the hydroformylation of olefins with rhodium complex were described. The new class of rhodium catalysts allows the use of low pressure and leads to high yield of product.
In EP 273,489 a process was disclosed for the selective carbonylation of conjugated dienes in the presence of a specific palladium compounds with a multidentate organic phosphorus ligand. According to this process also monodentate phosphorus compounds may be present. This process aimed at high conversion rates and less corrosion problems.
In EP 489,472 a carbonylation process was disclosed of ethylenically unsaturated compounds in the presence of a palladium catalyst, a monodentate phosphine, and an anion of derived from an acid with pKa less than +3 to maintain a high reaction as well as conversion rate.
In U.S. Pat. No. 5,994,591 a hydroformylation process was disclosed in the presence of a palladium, platinum, or nickel catalyst, a bidentate ligand, and anion other than halide anions to obtain a process for effectively removing the catalyst in a solventless evaporation product separation system without affecting the effectiveness of the catalyst.
In U.S. Pat. No. 6,037,506 a process was presented with a palladium, platinum, or nickel catalyst, a bidentate ligand, an acid, and a promoter comprising a formate or formic acid reagent. This process leads to less damage of the reactor. It was further reported that this process reduces the paraffin make.
Generally, such processes are conducted by introducing the various reactants into the reactor and allowing the reaction to proceed under the desired reaction conditions. The disclosed methods, however, suffer from a few disadvantages, i.e. the occurrence of solid particles on the liquid-liquid interface of the immiscible liquid phases (plating), and in many instances also the formation of paraffin side-products. These lead to decreased yields and cumbersome isolation procedures. Plating leads to loss of active catalyst during the process, and since the catalyst by far is the most expensive constituent of the reaction mixture plating effects are commercially unattractive. Therefore, in one aspect of the present invention plating is prevented effectively and the advantageous properties of the prior art methods are maintained.
To this end an anti-plating process was found for the hydroformylation of an ethylenically unsaturated compound process in the presence of an acid with a pKa less than +3, and a catalyst of a group VIII metal and a bidentate ligand of the formula:
R1R2xe2x80x94Pxe2x80x94Xxe2x80x94Pxe2x80x94R3R4xe2x80x83xe2x80x83(I)
wherein P is a phosphorus atom, X represents a bivalent organic bridging group, R1, R2, R3 and R4 represent independently a substituted or unsubstituted hydrocarbyl group, or R1 and R2 together with the phosphorus atom to which they are bonded and/or R3 and R4 together with the phosphorus atom to which they are bonded represent a bivalent substituted or unsubstituted cyclic group, characterized in that the process is performed in the presence of a mono tert-phosphine, wherein the ratio moles of mono tert-phosphine:moles of acid is from about 1:1 to about 10:1.
In addition to the effective anti-plating properties of the above process another aspect of the present invention provides a method for reducing paraffin make. By using a mixture of at least two acids wherein one of the acids has a pKa less than xe2x88x923, and another acid has a pKa value between xe2x88x923 and +3, the paraffin make is strongly reduced. By using such a mixture of acids without the addition of the mono tert-phosphine compound the paraffin make is also effectively reduced. However, the advantageous anti-plating effects are no longer observed.